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Broken bolt! Help!

5K views 58 replies 28 participants last post by  alan53 
#1 · (Edited)
Help! One of my connecting rod bolts broke off about half an inch inside my connecting rod. Was getting it up to torque, when the bolt snapped off. I learned my lesson and got myself a set of OEM bolts. Now the real problem: the broken bit didn't break flush, but rather at an angle (which makes it next to impossible to drill a pilot hole). I've tried left hand bits, trying to tap a chisel into the bolt with a friend holding the piston down from the spark plug hole, easyouts, and gone through about 6 regular drill bits. Haven't made any progress at all, and can't seem to figure out how to drill into metal that's at a jagged angle. Welding a nut in is obviously not an option and neither is drilling out and retapping. Can anybody provide some
input? Anything helps at this point. Thanks in advance.

Edit: I managed to get some photos of my situation, although the quality is not the best. In the photo is the broken part of my bolt inside the conrod, it's hard to see but the right side of the bolt is raised about a centimeter higher than the left side. |-_| <- is what it looks like if you could see through the rod from a side view.
 

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#3 ·
IF I had a complete machine shop I'd take a bolt with the same thread and drill a hole dead center. Then I'd use that as a guide to drill out the broken bolt. Then again, I don't have the equipment to do that properly so I'd remove the rod and piston and take them to a shop that could get it out...
 
#4 · (Edited)
This is a real challenge.. If you succeed in drilling you will likely mess up the threads of the connecting rod, requiring you to tap larger threads or the possible use of a heli-coil or time-sert, which would mess up the balance of the conn-rods, so neither is a good idea.

I am not sure where you are located (in the US), but I think I would simply buy a new used connecting rod off ebay and call it a day.
I think they (the connecting rods themselves) were different between M52TU, and 2.5 and 3.0 M54, so look into REALOEM. I don't remember if conn-rods are color coded, but I don't think so. I would use standard conn-rod bearings and plasti-gauge to confirm fitment when using a used conn-rod.
 
#8 ·
This is a real challenge.. If you succeed in drilling you will likely mess up the threads of the connecting rod, requiring you to tap larger threads or the possible use of a heli-coil or time-sert, which would mess up the balance of the conn-rods, so neither is a good idea.
I was more looking to drill a pilot hole in and use a reverse threaded bit to pull it back out, obliterating the broken bit and rethreading it somehow seemed far too sketchy for me. And I'm trying to get all the ideas I can before I have to resort to a new conrod...that would be a PITA.
 
#9 ·
Actually with the rod cap off, I have full access to the conrod and the broken bolt. I guess dropping the crank would help, but I believe that requires unbolting the trans and flywheel? Correct me if I'm wrong but it's just work I'm not really
up for to get a few more inches of clearance.
 
#15 ·
If that doesn***8217;t work you***8217;ll have to drop the crank and take the piston+con rod to a machine shop. Hey, just run on 5 cylinders like a Volvo. /s
Can I get the piston and conrod out through the bottom by dropping the crank? I had always thought it was imperative that you remove it after ripping off the head. If that's true I may have to start the process of removing the crankshaft...
 
#13 ·
If you can get old bearing caps from a wrecked engine at the wreckers, you could make a drilling jig and may get it out.

Parts you will need:

1. A few rod bearing caps.
2. Hollow pipe soft copper tubes should work.
3. Bolt twice the length of original cap bolt.
4. Various sizes of cobalt drill bits.
5. Pieces metal flat stock approx 3/4" x 1.5" x 1/16" etc.
6. C clamps

Procedure:

The idea is to set one cap on top of the other to make the drilling jig. In order to get it to fit properly onto of the bottom cap you will need to remove part of the center section of the cap going on top so it will mate nice and flat with the lower one. You will have to do it by trial and error, no other way to do it.

Once you get the two caps to mate properly you need to determine the length and diameter of inner pipe shim to make the center guide for the hole. The idea here is to insert say a 1/4" diameter pipe into the hole where you need to drill so it will act as a centering guide from the top of the hole to the top face of the broken bolt, and keep the bit from wandering. Ideally you want the drill bit to fit a bit loose inside the pipe but the pipe to fit snug inside the cap holes. Again, trial and error will find the closest sizes.

Depth of drilled hole (i.e. length of drill bits needed) can be determined by using a caliper and taking the depth of hole from the good side of the jig by simply holding it together by hand.

Once you have made the jig proceed as follows:

- Remove original cap.
- Install sacrificial cap in position.
- Place second sacrificial cap on top of first one. Using longer bolt tighten both caps down securely on the one side.
- Place metal shims on either side of both old caps where broken bolt is and tighten C clamp to keep them aligned. If the top cap does not sit flat on the drill side you may need to add a C clamp in the center to hold it down flat.
- Using the appropriate size cobalt bit (correct length and diameter) slowly drill the first hole to the required depth,
- Use same procedure to drill the next larger hole etc. until you get the size you need to use an extractor or even better try tapping the new hole with a left hand tap and use a left hand bolt to remove it.
 
#18 ·
If you can get old bearing caps from a wrecked engine at the wreckers, you could make a drilling jig and may get it out.
That is the idea I was going for, but unfortunately I don't have access to more rod caps. I was thinking about JB Welding a few aluminium spacers together to try and make a center guide and place it directly over the opening, but can't figure out a way to keep my drill and the end of the spacer tube from catching and flying all over the place...any idea about self-centering drill bit holders? If those even exist?
 
#14 ·
In theory if it was a clean break the rest of that bolt should just back out with no problem, but it would have been out by now. So either it was too long and bottomed out (not good when talking bolts), or what's left of the bolt is deformed and stuck in the hole. You need something to guide a drill down the center of the broken bolt. You'll probably need a machinists help. Get a bushing made that fits in the hole in the cap and use it to guide the drill. Basically what newbimer is suggesting above. These are cracked rod however, and I'm not sure about the idea of installing a cap that doesn't belong to the rod. If it's deep enough in the threaded hole you could do as moparjim suggests.

However! If this bolt was improperly heat treated and is extremely hard(which could be why it broke), you may have a very difficult time drilling it. 6 drills and nothing is leaning this way, unless they are harbor freight drills in which case you may as well be using a noodle. Check the other end of this broken bolt to see how hard it is. If a file cuts it with reasonable force, it should drill OK. To have any chance even if the bolt is not extremely hard, you need good cobalt steel drills (PTD, Dormer, Cleveland, etc.) and drill at slow speed <500RPM with oil. These drills would have split points, which reduces the force required to get the drill to cut. If, at this point there is already damage to the thread in the rod, I'd cut my losses and pull the head and replace the rod.
 
#19 ·
In theory if it was a clean break the rest of that bolt should just back out with no problem, but it would have been out by now. So either it was too long and bottomed out (not good when talking bolts), or what's left of the bolt is deformed and stuck in the hole. You need something to guide a drill down the center of the broken bolt.
What exactly do you mean by a bolt being too long and bottoming out? I reused the same bolt that was there when the car rolled out of the factory, so could it still have been "too long"? Sorry I don't know much about this kind of terminology lol.

unless they are harbor freight drills in which case you may as well be using a noodle. Check the other end of this broken bolt to see how hard it is. If a file cuts it with reasonable force, it should drill OK
That is a good idea, I'll try to experiment with the other half of the broken bolt.

I'd cut my losses and pull the head and replace the rod.
Thankfully I've been careful to not damage the threads at all, but it may have to come down to that if all else fails.
 
#20 ·
Pics would be good. Many of us have faced this and worse over the decades, but without a clear understanding of what you're up against, there's not much to gnaw on.
 
#25 ·
Get a screw that's the same size as the one that broke. Put it in a vice and drill a hole right down the middle of it. Put the cap back on the rod and tighten the good side a bit. Now slide the screw you drilled into the other cap hole and hold it with one hand. Drill with your other. Have a container with oil beside you so that you can dip the drill bit in it (often). Use only cobalt bits (not some crap from a big box hardware store), carbide is too brittle to use in a hand drill (it doesn't flex at all, just breaks and can not be drilled out when it does break). Drill the hole big enough so that you won't break an easy out in it, but not so big that the wall thickness of what's left is really thin and the easy out causes it to expand and swell up, making it tighter and harder to remove.
 
#26 ·
That's an awesome idea!! This might be the one that works. I could use another one of my extra conrod bolts as the guide, but now the question is how to get a hole through it seeing as I don't have access to a vice. I'm guessing trying to drill through it would take unbelievably long...maybe I'll try to see if Home Depot carries any bolts of the right length and thread but are already hollowed out. Thanks for the advice!
 
#28 ·
Honestly at this point I'd call a thread repair person. They have all the tools and experience and if they can't do it you most probably can't. I once torqued a bolt by more than 40nm and it deformed and I couldn't get it out after 2 hours of cursing. Thread repair guy came and got it off in about 10mins. Just my 2c. Normally they have two different prices, one for if they can get the bolt out and one if they can't.

P.s taking the head off is a LOT easier than removing the crank.
 
#42 · (Edited)
I will take this broken bolt out for you free of charge, so don't panic.

1) on this rod with the cap off, use a good bolt and thread it into the other rod hole to see if the bolt come through the hole threads: to see if the broken threaded shaft can come out to the top of the rod hole?
If yes then it's easier to turn it in CW and it will come out at the top. If not then it has to be turned CCW and out to the bottom.

2) buy an impact driver as this one: https://www.amazon.com/TEKTON-2905-...argid=aud-829758849484:pla-420785539586&psc=1
and use only the flat screwdriver bit.

3) with a sharp chisel and a hammer, hit the chisel on the broken bolt -- with someone pushing down on the piston using a wooden or plastic rod because a metal rod could damage the spark plug threads -- to score a line (the line should be aimed across the broken bolt as center as possible like a diameter line of a circle) . Take times and carefully doing this while waiting for the impact driver arrive, and try to score a good deep line. The hammering effect also help to loosen the bolt.
If (1) above is yes that the bolt can be threaded through the top, then while twisting the chisel CW and hammering the thing it may turn the bolt and out to the top.

If bolt cannot get out at the top then wait for the impact hammer , and use it to drive the bolt CCW with a hammer. (the impact driver bit needs to be sharpen down to match the chisel profile.)
 
#44 ·
Gday

I’m familiar with most of the methods mentioned here by posters and have done a lot of this during my work, in all honesty I’d call an expert in like others have suggested.
It’ll be easier, quicker and probably cheaper and they’ll have all the high quality gear to tackle the job.
It’s what we do in industry even though we could tackle the job ourselves.
By the time we’ve found all the gear in our workshops, made some stuff to help, the expert would have arrived and got the job done, meanwhile we are onto the next maint job etc.

You should have good access to competent, mobile bolt techs over in the US near most of your towns, cities I guess
 
#45 ·
Don't know if its be suggested.. But have you tried tapping it out with a center punch of some sort?
The threads should be clean, just need the ability to twist it back out.
I've taken a couple bolts out like this, hitting off center at an angle to impart a counter clockwise force.
 
#48 ·
Ok.... as someone else has said, you're gonna want to use the rod cap as the guide for the drill bit.

Take the cap to a hardware store or perhaps a machine shop and ask them if they have (or can make) a guide bushing that fits in the rod bolt hole. If you can find one that's a little too small you can always wrap the guide to make it fit tighter.

Once you have the guide, get a good drill bit (reverse).

Put the rod bearing back into the rod and cap and bolt the rod back onto the crank. You do not want to torque the bolt.... just snug it up.

This should put you in the position of having the rod and cap held in place with the guide being over the broken bolt.

Drill down through the guide and if you are lucky the drill bit will grab the broken bolt and reverse it out.

Even if it doesn't remove the bolt you will still be able to drill a hole in the center of the bolt which should allow you to use an easy out to grab the broken bolt.
 
#49 ·
That bolt will come out, but make sure you proceed with extreme caution. Once you get off center and drill into the rod, it's game over (obviously). This seems to happen 8/10 times I see someone try to drill something out, so try to be the exception.

You can forget about a left hand bit turning that thing out--highly unlikely. Forget about trying to weld anything onto that if you want to avoid pulling the rod/piston--if you can't drill it, it's unlikely that you're going to be able to weld that precisely in situ.

As others have said, you'll likely end up using the rod cap as a guide in some configuration or another, but your not really ready to do that since the broken bolt is now a mess.

If it were me, I would probably try to chuck a flat-topped carbide burr into a die grinder and see if I could flatten the top of that broken bolt just enough to get a click-style (or automatic) centerpunch to establish center on that broken bolt. Drill a pilot (but not too small, since a broken bit in there will only make matters much worse), and then drill out with a metric bit of the correct size. You could use a left-handed bit if you're feeling lucky. If you don't have a carbide burr, perhaps you have a dremel with one of those abrasive drums that could serve the same purpose. All you need to do it just get a flat land on that bolt large enough for a centerpunch. Use a good automatic punch, this isn't really the place for a hammer since it's likely you'll end up punching off center.

Just take it slow, your first priority is establishing a land on that top of that bolt head. Even if you had a nice jig setup with a guide sleeve or bushing, there's a decent chance that the bit will walk into the holes you've already drilled, or will drill out of round and give you an off center hole.

Good luck, you'll get it, just take your time and don't drill into the rod.

Also might be smart to put some tape on that bearing surface if you're going to be drilling and working so close to it. Some painter's tape will do.
 

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#50 ·
How about this: either find, or turn on a lathe, a piece of rod that fits snugly in the bolt hole of the bearing cap; use a drill press to drill a hole through the center to act as a guide for a top quality drill bit to drill an initial hole, then follow with your reverse drills. Ideally your guide would fit into the recess of the con rod bolt hole a little bit; if not a pair of vise grips could ensure that the cap stayed in position along with the unbroken bolt.
 
#51 ·
Had a similar situation with a head bolt in my 740. It sheared off about a 1/4***8221; down and on an angle. Drilled multiple screws that were the same size but couldn***8217;t get it to bite, not enough thread to catch. Couldn***8217;t get a drill to drill into the bolt and didn***8217;t want to mess up the threads in the block. I ended up using a pick and catching an edge on the screw and backed it out. Took a long time and had to keep going back and forth to ensure it doesn***8217;t bind but had success at the end. It***8217;s a pain but with patience and perseverance, it will come out assuming it***8217;s not jammed against the bottom where it screwed in.
 
#52 ·
I have had some luck using a small carbide cutter in a Dremel tool. Ball-end cutter can establish a depression in which a small drill bit can be carefully started - adjust center before starting drill bit. Also, once the bolt broke, tension was released and it may not take enormous torque to turn the bolt out. A small square-end burr can cut a slot for a screwdriver bit, even to use a hand impact driver.
Practice first and go slowly. If you slip, carbide will cut what it touches.
 
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